Control valve systems for controlling the flow of liquids and/or gasses in a process system are generally known in the art. These systems generally employ an actuator to open and close the control valve. The position of the control valve is generally controlled by a positioner. Volume boosters are generally included in the control valve system to improve the stroking speed of the actuator.
Manual override of the positioner to allow for manual control of the actuator and override of the positioner generally requires the use of a bypass value in fluid communication with the actuator. The bypass valve allows the pressure in the actuator to equilibrate, so that manual operation of the actuator is possible. For example, in a piston actuator, the bypass valve is generally disposed between first and second chamber portions of the cylinder. Once the pressure in the upper and lower cylinders has reached equilibrium, the piston is freely moveable in response to a manual operating device, such as a hand wheel.
FIG. 1 shows a typical bypass arrangement with a pneumatic bypass on a piston actuator. The bypass valve 10 is connected to the boosters 12, 14 and the actuator 16 by a tee 18 and pipe nipple 20. FIG. 2 shows a typical bypass arrangement with a hand wheel and bypass valve 10 disposed downstream of the volume booster 12. As in FIG. 1, the volume booster 12 is connected to the bypass valve 10 using a tee 18. Such arrangements create additional leak paths and increases fitting costs and assembly time.